Cleaning device



Oct. 19, 1965 c. M. FURGASON CLEANING DEVICE Filed May 28, 1963 Y POQ O 024m MR m wm M m W ym 7% Mflfl ON United States Patent 3,212,217 CLEANllNG DEVICE Carl M. Furgason, Houston, Tex., assignor to Tex-Tube, Inc., Houston, Tex., a corporation of Texas Filed May 28, 1963, Ser. No. 283,849 7 Claims. (Cl. 518) This invention relates in general to an abrasive blast cleaning device. More particularly, it concerns a new and improved gas powered abrasive blast gun which produces maximum velocity of abrasive particles with minimum wear of component parts of the gun.

The most common type of abrasive blast system in use at present, includes a blast gun connected to a flexible air pressure line with the abrasive supply connected to the system at some point along the flexible pressure line. In such systems a mixture of abrasive and pressurized air or gas is subsequently accelerated therefrom in a blast generally by a converging nozzle at the end. An inherent disadvantage of such systems is excessive wear caused by the highly deleterious mixture of abrasive and pressurized gas on the flexible pressure line to the gun. This results in short life for the system and the necessary expense in replacement of pressure lines and other parts thereof.

This disadvantage has been overcome in the past by delaying the injection of abrasive into the system and, in particular, by injecting abrasive into the system at the blasting gun itself. With this solution, it has been found beneficial, in the prior art, to inject the abrasive into the blasting device through a conduit parallel to and coaxial with the flow of pressurized gas through the gun. Advantages realized by this innovation lie in the fact that a blanket of air is provided around the walls of the device, the blanket tending to insulate the walls of the gun from contact with the abrasive thereby providing extended life for the parts of the device. Examples of apparatus utilizing this principle are disclosed in the United States Patents 992,144 and 2,369,576.

While the above mentioned improvements help to mitigate wear in the system, the delay of injection of abrasive into the pressure flow, in itself, produces addi tional problems. Thus, delay of abrasive injection until just prior to discharge, shortens the length of time for the abrasive to be accelerated from the injection velocity to the velocity of the blast medium so full acceleration of the abrasive particles is not obtained. This results in a lower velocity discharged abrasive than would normally be available from flow at a given gas pressure. Another problem generated by such modified systems results from the presence of the blanket of air surrounding the stream of abrasive which, although providing the benefit of preventing abrasion of the walls of the chamber, also, due to the close proximity to the discharge point of the sys temftends to concentrate the stream of abrasive. This results in discharge of an incompletely mixed stream of pressurized gas and abrasive material. The discharged abrasive and gas then takes on the character of a core of abrasive surrounded by an annulus of gas and provides spotty, concentrated type of blast cleaning rather than the more dispersed blasting which would be obtained with even mixture of the components.

It is therefore an object of this invention to provide an abrasive blasting device which incorporates the benefits of the above-mentioned systems While avoiding their inherent disadvantages.

It is another object of this invention to provide an abrasive blasting device which discharges a well-dispersed, high velocity blast of abrasive and provides a maximum service life with a minimum of Wear on the component parts thereof.

Patented Oct. 19, 1965 It is still another object of this invention to provide an abrasive blasting device which can thoroughly mix particulate abrasive with the blasting medium immediately prior to discharge of the mixture from the device.

It is yet another object of this invention to provide an abrasive blasting device which is economical to manufacture and yet is durable and incorporates components which are easily replaceable with a minimum of expense and difliculty.

It is a further object of this invention to provide an abrasive blasting system in which abrasive is introduced proximate the discharge point of the system yet is thoroughly mixed with the blast medium to provide suitable dispersion thereof and in which the abrasive is accelerated to a velocity substantially equal to that of the blasting medium.

These objects are accomplished according to the present invention by formation of an abrasive blasting system to comprise a pressurized gas supply line, a blast nozzle, a venturi section between the gas supply line and the nozzle and an abrasive particle supply tube coaxially disposed with relation with the throat of the venturi so that in use an annular sheath of pressurized gas is supplied around the abrasive supply tube and through the throat of the venturi. This is followed by a plenum-type chamber to allow re-expansion of the blast medium and mixing of the medium and the abrasive particles. The plenum chamber of the device then communicates with a gradually converging nozzle wherein the mixture is reaccelerated for discharge from the device. The combination provides for ejection of the abrasive into the system without imposing undue wear upon the venturi component, yet provides, through the plenum chamber, a means for suitable mixing of the abrasive material with the medium. The gradually converging nozzle of the system provides for gradual reacceleration of the medium with attendant acceleration of the abrasive material to provide acceleration of abrasive material to a velocity substantially equal to that of the medium.

Other objects and attendant features of the invention will be better understood to those skilled in the art upon consideration of the following detailed description when considered in conjunction with the accompanying drawings wherein:

FIG. 1 is a schematic diagram of a system embodying the invention connected to the blasting device of FIG. 2.

FIG. 2 is a sectional side view of an abrasive blasting device embodying the features of the invention.

Referring now more specifically to FIG. 1 of the drawing, a sandblasting gun indicated generally at 2, is shown connected to an air pressure supply line 4 which in turn is controlled by suitable valve means 6 for connection and disconnection of the device to pressurized gas source 8. Sand pct 10 serves as a reservoir for the abrasive blasting material which may be fed to injection line 12 by gravity feed. Motivation to transport the abrasive material to sandgun 2 is provided by low pressure air tapped from line 4 through a suitable connection 14 Referring now to FIG. 2 of the drawing, said supply from line 12 is injected into gun 2 through injection tube 16 disposed coaxially with the bore of the gun through the base thereof. Base member 18 serves as a connection to air pressure supply line 4 through nipple 20 and also provides a hand grip for the operator of the gun. Sealing for the intersection of the injection tubes and the wall of base member 18 may be provided in any suitable manner and is shown here provided by support member 22 brazed or soldered to the wall of the base member 18 as shown. An 0 ring 24 is provided around injection tube 16 to insure a pressure-tight seal.

Tubular housing 26 is removably connected to the forward end of base member 18 through threaded connector 28. Housing member 26 contains, in succession, the following removable members: Converging nozzle 30, diverging nozzle 32 having a short cylindrical section 33 in its throat, and tubular insert 34. The entire assembly is connected to one another and in turn to a retaining ring 36 suitably fixed in the mouth of housing 26 as shown. Tubular insert 34 is provided with a recess 38 in the forward peripheral wall thereof in which nozzle member 40 is seated and retained.

As shown in the drawings, nozzles 30 and 32 are arranged to provide a converging-diverging or venturi-type of nozzle near the base of housing 26. The tubular insert 34 provides a cylindrical plenum chamber and nozzle mount forward of the venturi. Nozzle 40 furnishes a discharge point forward of the chamber. The interior diameters of these members are such that the interior peripheral surfaces from smooth junctures at the abutting surfaces thereof. Connection between these members may be made in any suitable fashion such, for example, as the threaded fasteners shown in the drawing. rings 42 and 44 are provided in nozzles 30 and 32 respectively to prevent by-pass leaking of the pressure medium between the outer walls of the removable members and the inner wall of housing 26 and leakage into the throat of the venturi.

Nozzle 40 is characterized by a gradually converging nozzle section 46 and a cylindrical throat section 48. This nozzle should have a sufficiently low taper to provide time for acceleration of the abrasive particles yet should not be unduly long so as to result in excessive boundary layer skin drag which would decrease the efficiency of the device.

The throat diameter of nozzle 40 should be such that the most efficient expansion is obtained and is limited in minimum value to a diameter which will produce a velocity below the acoustic velocity for the gas flow.

The smooth juncture between nozzle 40 and tubular insert 34 provides continuity in the surfaces and reduces wear in the entrance to the nozzle.

In operation of the system, pressure is introduced into gun 2 from pressure source 8 through operation of valve 6. Pressure in injection line 12 moves sand fed from sand pot to injection tube 16 providing a high density, low velocity supply of sand to the gun. Air under pressure is directed through base 18 to converging nozzle 30 where it is accelerated with an attendant drop in pressure until it reaches the minimum point of convergence at a minimum pressure and maximum velocity. The resulting pressure at this point is somewhat effected by the presence of the end of tube 16 near the throat of the converging nozzle, since this obstruction tends to further reduce the effective diameter of the throat thereof. This pressure can be varied by varying the proximity of the end of the tube with respect to the throat. This variation is provided for, in this embodiment of the invention, by slidable engagement between housing 22 and tube 16. Suitable means such, for example, as set screw 50, may be provided to fix the position of tube 16 as desired. Abrasive 52 is ejected from the end of tube 16 into the low pressure, high velocity flow through the throat of nozzle 30 by pressure bled from line 4 through injection line 12 and by the low pressure condition of the blast medium itself. Due to the presence of tube 16 an annular blanket of air is formed around the walls of the nozzles and the sand is ejected essentially as a central core contained therein. The core of abrasive then is expanded through the diverging section 32, the velocity of the air decreasing, due to compression, until the chamber formed by cylindrical insert 34 is reached. This decrease in the velocity of the air provides an opportunity to decrease the differential in velocity between the sand discharged from tube 16 and the blast medium. The diverging section 32 provides an opportunity for the core of abrasive sand to be expanded and dispersed throughout the chamber until uniform mixture of the components has been achieved. After mixing, the components enter the gradually converging nozzle section of nozzle 40 whereupon the mixture is gradually accelerated until maximum velocity is achieved at the throat section thereof. The gradual tapering of this nozzle section provides an opportunity for the abrasive 52 to reach a velocity essentially equal to that of the blast medium prior to discharge through cylindrical throat section 48 for subsequent blast cleaning of a surface.

Any suitable pump or compressor may be used as a source of pressure and it is specifically contemplated in this invention that compressor bleed air from a gas turbine as illustrated in the process and apparatus of copending application Serial No. 283,848 will be utilized in conjunction with this invention.

The schematic diagram of FIG. 1 is intended as illustrative only and can be varied in any suitable manner without altering the scope of the invention.

Although the nozzle and insert components could be made integral with the structure of housing 26, it is preferable, for replacement purposes, that they be easily removable as shown to provide inexpensive component replacement when wear eventually decreases their effectiveness.

The relative dimensions of the component parts, of course, may be varied, as desired, to provide the most effective results.

The materials may be of any type suitable for use with the environment of the device. Materials embodying suitable strength, wear and weight characteristics such, for example, as 6061 T6 aluminum are contemplated for use in the tubular housing 26 and base 18 and for the nozzle and tubular insert members 30, 32, 34, as well as the retaining ring 36. Since nozzle member 40 is subjected to the direct action of the abrasive blast, it should be fabricated of a material extremely resistant to abrasion such, for example, as white cast iron and particularly high molybdenum or high chromium white cast iron, sintered tungsten carbide, silicon carbide, or material having similar properties.

Although the device described has, in terminology, been limited to the use of sand and air, it should be obvious that a suitable motivating fluid or liquid could be utilized in conjunction with the device. Similarly, any other particulate material could be substituted for the sand for abrasive cleaning therewith or even shot peening or like processes. It has also been found that by utilizing air or any other gas as a motivating force and injecting a liquid through injection tube 16, the device provides an effective spray gun for producing a very large fog for fire fighting, protection of citrus from freezing, or like uses.

The invention thereby provides a device for effectively producing a thoroughly mixed spray of abrasive or other material and pressurized fluid; and, in the case of abrasive materials, accomplishes this While avoiding abrasive contact with a maximum number of the components of the system. There are obviously many other advantages realized by use of this invention and what is described above is intended solely as exemplary of specific applications utilizing the precepts of the invention. It therefore should be understood that, within the scope of the appended claims, the invention may be practiced otherwise than as specifically described.

What is claimed is:

1. A material mixing and spraying device comprising,

an elongated housing means conducting a pressure fluid to one end of the housing,

a venturi coaxially disposed in said housing adjacent to said end,

a conveying means for conducting a material to said device including a material supply tube through said end coaxially disposed with relation to and terminating adjacent the smallest diameter section of said venturi to inject particulate abrasive material into the fluid flowing therethrough,

said housing having in succession a cylindrical mixing chamber next adjacent said venturi to provide mixing of said material and said fluid and to diminish the velocity diflerential therebetween,

and a gradually tapering converging frusto conical nozzle to provide gradual acceleration of said abrasive material and said fluid prior to discharge from said device.

2. A sandblasting gun comprising,

an elongated housing, means conducting air to one end of the housing,

a venturi coaxially disposed in said housing adjacent to said end,

a conveying means for furnishing sand to said device including a sand supply tube through said end coaxially disposed with relation to and terminating adjacent the throat of said venturi to inject sand into the air flowing therethrough,

means to vary the position of the end of said tube with relation to the smallest diameter section of said venturi to vary the quantity of sand injected into said air,

said housing further having in succession a cylindrical mixing chamber next adjacent to said venturi to provide mixing of said sand and said air and to diminish the velocity diflerential therebetween,

and a gradually tapering frusto conical converging nozzle to provide acceleration of said sand and said air prior to discharge from said gun.

3. A sandblasting gun in accordance with claim 2 wherein said conveying means comprises a line connected to said tube,

a sand reservoir adapted to gravity feed sand into said line,

said sand being drawn through said line by said venturi.

4. A sandblasting gun in accordance with claim 2 wherein said conveying means comprises a line of smaller diameter than said air pressure line connected at one end to said tube and at the other end to said air pressure line to provide air flow through said line of smaller di ameter at a lower pressure than that of said air pressure line,

a sand reservoir disposed intermediate the ends of said line of smaller diameter and adapted to gravity feed sand thereto,

whereby sand is conveyed to said tube by said lower pressure air,

5. A sand blasting device comprising a pressurized gas supply line,

a nozzle to emit a blast of gas suspended abrasive particles at high velocity,

a tubular conduit joining said nozzle to said supply line,

said conduit comprising a constriction spaced upstream from said nozzle concentric with the conduit,

a first portion which tapers outwardly from said constriction upstream thereof,

a second portion which tapers outwardly from said constriction downstream thereof,

a third portion which tapers outwardly from said nozzle upstream thereof,

and a fourth portion of uniform cross-section substantially throughout its length joining the downstream end of said second portion to the upstream end of said third portion,

all of said portions being coaxially aligned with said nozzle and said constriction,

and an abrasive material supply tube having its outlet end positioned within said first portion coaxially with said constriction.

6. A sand blasting device as claimed in claim 5 comprising means to permit said abrasive material supply tube outlet end to be moved toward and away from said constriction on the locus of the centers of said constriction and said nozzle.

7. A sand blasting device as claimed in claim 5 wherein the cross-sectional area of said constriction is greater than the cross-sectional area of said nozzle and less than about one-half the cross-sectional area of said fourth portion.

References Cited by the Examiner UNITED STATES PATENTS Re. 23,064 12/48 Tirrell 51-11 818,776 4/06 Murray 5l11 992,144 5/11 Babcock 51--11 1,107,244 8/14 Carter 5111 2,462,480 2/49 Eppler 518 2,503,743 4/50 Keefer 51- 11 FOREIGN PATENTS 646,861 7/28 France.

LESTER M. SWINGLE, Primary Examiner. I. OVE RI- IOLSER, Examiner, 

1. A MATERIAL MIXING AND SPRAYING DEVICE COMPRISING, AN ELONGATED HOUSING MEANS CONDUCTING A PRESSURE FLUID TO ONE END OF THE HOUSING, A VENTURI COAXIALLY DISPOSED IN SAID HOUSING ADJACENT TO SAID END, A CONVEYING MEANS FOR CONDUCTING A MATERIAL TO SAID DEVICE INCLUDING A MATERIAL SUPPLY TUBE THROUGH SAID END COAXIALLY DISPOSED WITH RELATION TO AND TERMINATING ADJACENT THE SMALLEST DIAMETER SECTION OF SAID VENTURI TO INJECT PARTICULATE ABRASIVE MATERIAL INTO THE FLUID FLOWING THERETHROUGH, SAID HOUSING HAVING IN SUCCESSION A CYLINDRICAL MIXING CHAMBER NEXT ADJACENT SAID VENTURI TO PROVIDE MIXING OF SAID MATERIAL AND SAID FLUID AND TO DIMINISH THE VELOCITY DIFFERENTIAL THEREBETWEEN, AND A GRADUALLY TAPERING CONVERGING FRUSTO CONICAL NOZZLE TO PROVIDE GRADUAL ACCELERATION OF SAID ABRASIVE MATERIAL AND SAID FLUIS PRIOR TO DISCHARGE FROM SAID DEVICE. 